Image sensors have become ubiquitous. They are widely used in digital still cameras, cellular phones, security cameras, as well as, medical, automobile, and other applications. The technology used to manufacture image sensors has continued to advance at a great pace. For example, the demands of higher resolution and lower power consumption have encouraged the further miniaturization and integration of these devices. While advances in pixel design have dramatically improved image sensor performance, several optical limitations have proved difficult to overcome by optimizing pixel circuitry alone.
Chemical mechanical polishing (CMP) is integral to semiconductor device fabrication. It can be used to thin wafers, remove excess deposition flux, and planarize surfaces. Further, the polish rate is selective to the composition of the films on the surface. Since CMP may be less precise than other fabrication techniques and is generally rougher on the semiconductor wafers, CMP may induce defects into electronic devices if not properly controlled. Defects may include pitting of the wafer, scratches on the wafer surface, and the destruction of layers of device architecture. Accordingly, optimizing the CMP process is desirable in electrical device fabrication.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.